22 Method of conducting the Canal Surveys. 



ner-posts of their abutments — those to the locks to the lines passing 

 through the centers of the two nearest quoin-posts, and those to the 

 aqueducts to the faces of their abutments. 



5. Offsets for determining the breadth of ground occuf^ied by the 

 Canal, were made from the base line at each angle or station and like- 

 wise at every other point where a variation in the breadth of the Ca- 

 nals required. The directions of the offsets were such as to bisect 

 the angles formed by the two portions of the base line situated con- 

 tiguous to them on each side, or in other words, the directions of the 

 offsets at the several stations were such as to bisect the angles form- 

 ed by the alignments, on the towing-path, the intermediate offsets be- 

 ing described perpendicular to, and the distances upon both reckoned 

 from the same alignments in links. 



6. The offsets on one side, across the towing-path, w^ere made 

 to extend at least twenty links (that being the minimum fixed by the 

 commissioners) and in every case to reach to the base of the out- 

 er slope of the embankment. The offsets in the opposite direction, 

 across the Canal, were made to extend at least fifteen links from the 

 margin of the water, that being the minimum allowance for the breadth 

 of the berm, and in every case to reach to the base of the exterior 

 slope of the embankment, if any, upon that side. 



7. Wherever an enlargement in the breadth of the Canal render- 

 ed the method of offsets inconvenient or impracticable, the portion 

 included in said enlargement was surveyed in the usual manner by 

 measuring the courses and distances of the several lines that enclosed 

 it on the side opposite to the towing-path. 



8. The survey embraced within its limits all grounds pertaining to 

 the Canal including all tracts or lots of land, set apart or appropriated 

 for the purposes of lock-houses, weigh-locks, collector's offices, &;c. 

 with llie names of the former owners and the date of each separate title 

 inserted as far as the same could be ascertained. 



9. The results of the measurements made as above described were 

 inserted in a field-book prepared as represented In the annexed draw- 

 ing, Fig. 1. Each page of the book was ruled into parallel lines as 

 aa', hh', Stc. one fourth of an inch distant from each other. Near the 

 center of each page and at right angles with those lines a red line as 

 AB was drawn extending across all the pages of the book. 



10. The red line thus drawn represented the base line of the sur- 

 vey. The portion of this line as KD or DH corresponding to any 

 given alignment, was made to embrace in its length as many of the 



